Boom and feedline construction for multielement antenna

ABSTRACT

A boom for supporting the radiating elements of a log periodic antenna is constructed as a unitary tubular structure comprising two or more flat or angled conductor strips insulated from each other and having longitudinally extending outwardly opening grooves therein. The antenna elements are directly mechanically and electrically connected to the flat surfaces of the strips which conduct electrical energy between the elements and external feedlines. The strips are mechanically interconnected by longitudinally spaced electric insulator blocks disposed internally of the boom. The blocks also serve as a mechanical support to which the sets of elements are connected along the boom. The external grooves stiffen the strips and additionally provide channels in which the feedline may be externally disposed for a connection to the strips in a manner to provide a balanced feed for the elements on opposite sides of the boom.

United States Patent [72] Inventor Gabriel John Enyedy & Sammy N. Watkins Palo Alto, Calif. Cupertina, Calif. [21 Appl. No. 847,043 [22] Filed Aug. 4, 1969 [45] Patented Apr. 27, 1971 [73] Assignee Sylvania Electric Products Inc.

[54] BOOM AND FEEDLINE CONSTRUCTION FOR MULTIELEMENT ANTENNA 2 Claims, 5 Drawing Figs.

[52] U.S. Cl 343/792.5, 343/797, 343/884 [51] Int. Cl ..H0lq 11/10, HOlq 1/12 [50] Field of Search 343/810, 811, 812, 816, 905; 343/7925, 797, 884

[56] References Cited UNITED STATES PATENTS 2,587,146 2/1952 Cross 343/884 343/792.5

3,259,904 7/1966 Blonderet al.

Primary Examiner-Eli Lieberman AttorneysNorman .l. OMalley, John F. Lawler and Russell A. Cannon ABSTRACT: A boom for supporting the radiating elements of a log periodic antenna is constructed as a unitary tubular structure comprising two or more flat or angled conductor strips insulated from each other and having longitudinally extending outwardly opening grooves therein. The antenna elements are directly mechanically and electrically connected to the flat surfaces of the strips which conduct electrical energy between the elements and external feedlines. The strips are mechanically interconnected by longitudinally spaced electric insulator blocks disposed internally of the boom. The blocks also serve as a mechanical support to which the sets of elements are connected along the boom. The external grooves stiffen the strips and additionally provide channels in which the feedline may be externally disposed for a connection to the strips in a manner to provide a balanced feed for the elements on opposite sides of the boom.

PATENT E DhPnzv I97! SHEET 1 (IF 3 wi h l Ii l A n N m o INVEN'TQRS GABRIEL JOHN ENYEDY SAMMY N. WATKINS BY 2 ATTORNEY PATENTEDAPRZTIHYI I 3576.580

" sumanFa INVENTORS I GABRIEL JOHN ENYEDY SAMMY N. WATKINS ATTORNEY PATENIEDAPRZYIQYI 3.576580 SHEET 3 UF 3 lea-WV l8 4 -35b g 38-- 34b 22 INVENTORS 37 I8 GABRIEL JOHN ENYEDY SAMMY N. WATKINS I ATTOR N EY BOOM AND FEEDLINE CONSTRUCTION FOR MULTIELEMENT ANTENNA BACKGROUND OF THE INVENTION This invention relates to log periodic antennas and more particularly to the construction of a boom to which the antenna elements are connected.

Log periodic antennas utilizing dipole arrays are generally elongated structures with antenna elements projecting radially from and spaced along the longitudinal axis of the antenna. Typical log periodic antenna structures of .this design are described in US. Pat. Nos. 3,113,316 and 3,123,827. The dipole elements must be rigidly supported along the axis of the antenna in order to occupy fixed spatial positions andalso must be coupled to feedlines over the length of the antenna in such a manner that complementary halves of each dipole are fed 180 out-of-phase with each other and adjacent dipoles are fed 180 out-of-phase with each other. In the past, accomplishment of these two functions, mechanical support and electrical'feed, has generally resulted in relatively complicated unwieldy structures that are costly to build and difi'rcult to assemble. I

Assembly of such antennas is further complicated by the need for efficient electrical coupling between the feedline and the elements as well as rigid mechanical support of the elements'. If the elements are capacitively coupled to the feedline, antenna assembly procedure is time consuming and difficult because of the critical spacing between each element in the line. If the elements are directly electrically connected to feedlines by brazing, soldering, etc., the difficulty of fabricab ing such arrays in the field renders impractical the use of a collapsible antenna design to facilitate assembly and disassembly of large antennas for convenience in transporting and handling them.

An additional factor in the construction of antennas of the type described above is the desirability of running the feedlines from the supported end of the boom to the remote end or feed point. A prior antenna described in the copending application of W. F. Schick et al., Ser. No. 598,251, now US. Pat. No. 3,518,690, assigned to the assignee of this invention, provides a feedline in the form of coaxial cable disposed inside the boom. While such construction provides a protective enclosure for the cable, it generally requires that the cable be mounted prior to mechanical interconnection of the strips to form the boom since the outer conductor of the coaxial line is electrically connected to one of the strips at several longitudinally spaced points. Such assembly technique is awkward and inconvenient, especially when performed on site in the field.

A general object of the invention is the provision of a lowcost log periodic antenna which may be rapidly and conveniently assembled in the field.

A further object is the provision of such an antenna that is configured to provide a high strength-to-weight ratio while also uniquely providing for external mounting of the feedlines.

Still another object is the provision of a rigid boom construction which has a high strength-toweight ratio achievable with a minimum of structural components.

SUMMARY OF THE INVENTION These objects are accomplished with a boom having corrugated strips. with longitudinal grooves and mechanically secured to internally disposed insulator blocks at longitudinally spaced intervals. Feedlines are disposed in one or more of the strip grooves externally of the boom and thus may be inserted after assembly of the boom. The corrugated strips not only increase the strength-to-weight ratio but also uniquely mechanically interlock with corresponding grooves in the insulator blocks so as to insure proper interstripspacing and additionally to strengthen the entire boom assembly.

DESCRIPTION OF THE DRAWINGS on line 5-5 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 shows a log periodic antenna 10 comprising an elongated longitudinally extending boom 12 supporting a vertical set 13 and a horizontal set 14 of dipole elements. As shown, boom l2 is mounted with its axis Aextending horizontally and is adapted to be supported at one end by a flanged mounting bracket 16 which preferably is electrically insulated from an adjacent supporting member, not shown. It will be understood that .the terms vertical" and horizontal' are descriptive of these parts of an antenna in but one of many operative positions, namely, when the antenna is vertically and horizontally polarized as shown in the drawing. These terms, however, are intended merely to define relative positions of the two dipole sets and the boom for a typical antenna orientation and are not to be construed as limiting terms. The axis A of the boom, for example, might be oriented to extend vertically with both sets of dipoles lying in horizontal planes. I

Both sets 13 and 14 of dipole elements project from the boom in planes perpendicular to the axis A with element length and interelement spacings decreasing from a maximum at end E of the boom to a minimum adjacent end F, the feed point end, in progressive increments at a predetermined ratio that defines the well-known characteristics of a logarithmically periodicantenna. The boom itself comprises balanced feedlines for all of the dipole elements and the spacing between the feedlines of each pair preferably is constant over the length of the antenna. The vertical and horizontal dipoles are connected to the boom by holders l8 and the dipoles which operate at the same wavelength are located at the same axial location on the boom.

In a preferred embodiment of the invention, boom 12 com prises four substantially identical longitudinally extending electrically conductive strips or plates 20, 21, 22 and 23, see FIGS. 2 and 3, arranged symmetrically about axis A in opposed pairs with one pair of strips 20, 22 lying in planes perpendicular to the planes of the other pair'of strips 21, 23. Each strip is formed with longitudinally extending inwardly projecting corrugations or grooves 25 and 26 which substantially increase the strength-to-weight ratio of the strip and thus the boom. These grooves project inwardly from the outer surface of the strip which otherwise retains its flat shape to facilitate mounting of holders 18. The strips are mechanically connected by screws 27a,and nuts 27b to longitudinally spaced rectangularly shaped tubular insulator blocks 28 having recesses 29 and 30 formed in each side surface for receiving and interlocking with the grooved portions 25 and 26, respectively, of each strip. The relative spacings of strip corrugations 25 and 26 and block recesses 29 and 30 are such as to maintain the desired spacing between the edges of adjacent strips which is securely abutted against the flat outer surface of the strip by screws 32 which extend through the strip and engage block 28. Thus the blocks 28 provide additional backup support for connection of antenna elements to the boom.

In a log periodic antenna using dipole arrays, adjacent dipoles along the axis of the antenna typically are. fed 180 out-of-phase with each other in order to propagate (or receive) electromagnetic waves unidirectionally, that is, along the axis of the antenna. The phase reversal of adjacent dipole elements in each set is achieved simply by reversing the direction of propagation of adjacent dipole elements connected to the same longitudinal strip on the boom. Thus, element 13 at the left in FIG. 3 extends upward (as viewed) from the boom strip 21 and each longitudinally adjacent dipole element connected to strip 21 extends downwardly therefrom. Since opposed strips 21 and 23, as well as strips and 22, are electrically conductive members andare connected to the dipole elements of each set, each pair of strips comprises a balanced feedline for one set of dipoles as well as principal structural member of the boom.

In order to electrically connect the antenna to external circuits, two pairs of feedlines in the form of coaxial cables 34 and 35 are disposed within grooves 26 of boom strips 20 and 21, respectively, externally of the boom and extend longitudinally thereof from the supported end E to feed point end F. The outer conductor 34a of cable 34, see FIG. 4, is directly electrically connected to the outer surface of strip 20 by antenna element holders 18 which serve as clamps to press and hold the cable against and securely within the groove of the strip. Additional means such as brazing or soldering may be used to insure and effective electrical connection of these parts. Similarly, the outer conductor of coaxial cable 35 is connected to boom strip 21.

The inner conductor of each coaxial cable at the feed point end F of the boom is electrically connected to the strip opposite from the strip to which the outer conductor of that cable is connected. Thus, inner conductor 34b of coaxial cable 34, see FIG. 5, is connected to conductive strip 22 at 37 and inner conductor 35b of cable 35 is connected to strip 23 at point 38. A plastic or rubber cap 39 protectively covers the feed point end of the boom.

The characteristic impedance of each pair of strip transmission lines forming the boom is an important factor in coupling energy to the dipole elements. ln order to design the boom with optimum impedance characteristics, the spacing between adjacent longitudinal edges of each pair of adjacent strips is precisely established and maintained. Such control of the interstrip spacing provides control of the magnitude of the shunt capacitance between opposed strips and thus enables control of the characteristic impedance of those strip lines. The corrugated construction of the strips and their interlocking relationship with the recesses of the insulator blocks 28 readily establishes the proper interstrip spacing upon assembly of the boom and thereafter.

The embodiment of the invention shown in F 168. l, 2 and 3 with vertically and horizontally polarized sets of dipoles supported and fed by the same boom is exemplary of the simplicity and ruggedness of the antenna construction afforded by the practice of this invention. Through the provision of corrugations in the strips, the strength-to-weight ratio of the boom is not only increased but rigidity of the entire boom is enhanced by the secure mechanical interlocking of the strip grooves in the insulator block recesses. This construction further simplifies assembly of the boom by permitting installation of the coaxial feedlines in the grooves of the strips after boom has been assembled. The provision of removably connectable dipole elements permits the antenna to be readily disassembled for convenience in shipping and handling in the field.

Efiicient direct electrical coupling between antenna elements and feedlines is also afforded by the mechanical connection between each holder 18 and the associated strip. These holders additionally serve as retainers or clamps for the externally mounted feedlines in the strip grooves. The antenna shown in FIGS. 1, 2 and 3 may be operated ll'l either the vertically, horizontally, circularly polarized modes through appropriate switching of the feedlines in the well-known manner. The invention may also be practiced with only one series of dipoles, either horizontally or vertically polarized, which are energized by one coaxial feedline and are mounted on a pair of opposed boom strips. In this case, a pair of angle-shaped strips are provided as suggested in FIG. 3 by the broken line interconnection of strips 20 and 23 at corner 42 and strips 21 and 22 at corner 43. The one series of dipoles are secured to these strips in longitudinally alternating relationship as described above.

lclaim: 1. An antenna comprising: an elongated tubular boom having an axis,

said boom comprising at least a pair of longitudinally extending electrically conductive strips and insulator blocks disposed internally of the strips for mechanically coupling and electrically insulating the latter relative to each other to form the wall of the unitary tubelike structure, said strips and blocks having complementary interlocked grooves and recesses, respectively, the grooves in each strip being coextensive with the strip and projecting inwardly toward said boom axis, a plurality of axially spaced antenna elements coupled to said strips, respectively, and a pair of feedlines electrically connected to the strips,

respectively, whereby electrical energy is transmitted between said antenna elements and the feedlines,

said feedlines comprising a coaxial cable disposed in one of said grooves and having outer and inner conductors connected to opposed strips, respectively.

2. The antenna according to claim 1 with a holder mechanically and electrically connected to each antenna element, said holder being mechanically and electrically connected to one of said strips across the grooves therein whereby to clamp said cable within a groove. 

1. An antenna comprising: an elongated tubular boom having an axis, said boom comprising at least a pair of longitudinally extending electrically conductive strips and insulator blocks disposed internally of the strips for mechanically coupling and electrically insulating the latter relative to each other to form the wall of the unitary tubelike structure, said strips and blocks having complementary interlocked grooves and recesses, respectively, the grooves in each strip being coextensive with the strip and projecting inwardly toward said boom axis, a plurality of axially spaced antenna elements coupled to said strips, respectively, and a pair of feedlines electrically connected to the strips, respectively, whereby electrical energy is transmitted between said antenna elements and the feedlines, said feedlines comprising a coaxial cable disposed in one of said grooves and having outer and inner conductors connected to opposed strips, respectively.
 2. The antenna according to claim 1 with a holder mechanically and electrically connected to each antenna element, said holder being mechanically and electrically connected to one of said strips across the grooves therein whereby to clamp said cable within a groove. 